Lithium difluorophosphate, LiPO2F2, is useful as electrolyte salt or additive for an electrolyte composition comprising an electrolyte salt for lithium ion batteries. Thus, WO 2008/111367 discloses how to manufacture a mixture of LiPF6 and LiPO2F2 from a halide other than a fluoride, LiPF6 and water. The resulting salt mixture, dissolved in aprotic solvents, is used as an electrolyte solution for lithium ion batteries. EP-A-2 061 115 describes, as state of the art at that time, the manufacture of LiPO2F2 from P2O3F4 and Li compounds, and, as invention, the manufacture of LiPO2F2 from LiPF6 and compounds with a Si—O—Si bond, e.g., siloxanes. US 2008-305402 and US 2008/102376 disclose the manufacture of LiPO2F2 from LiPF6 with a carbonate compound; according to US 2008/102376, LiPF6 decomposes at 50° C. and above under formation of PF5; according to other publications, PF5 is only formed at and above the melting point of LiPF6 (˜190° C.). EP-A-2 065 339 discloses how to manufacture a mixture of LiPF6 and LiPO2F2 from a halide other than a fluoride, LiPF6 and water. The resulting salt mixture, dissolved in aprotic solvents, is used as an electrolyte solution for lithium ion batteries.
However, the above methods are technically difficult and produce a greater amount of a by-product such as LiF which is not industrially interesting and thus would incur additional cost for the waste treatment. Further the starting material, LiPF6, is expensive and thus its use increases the production cost. Consequently, there has been a need to develop new processes, which are capable of avoiding the drawbacks indicated above.